(1) Field of the Invention
The present invention relates to a human identification apparatus which judges whether or not a human image included in one image sequence and a human image included in another image sequence represent the same person, and an apparatus which searches for or tracks a person.
(2) Description of the Related Art
In order to search for or track a specific person in an image sequence obtained by a surveillance camera, it is required to identify the specific person, namely, to judge whether or not a person that appears in one image or image sequence is as same as a person that appears in another image or image sequence.
One of the conventional methods for judging a person for identification with the view to searching for or tracking a person represented by a human image in an image sequence is to correspond human image areas in the neighboring frames (for example pp. 3 and 6 and FIGS. 2 and 9, in the Japanese Laid-Open Application No. 2003-346159).
FIGS. 1A through 1C are diagrams for describing the searching/tracking method described in the above-mentioned Application No. 2003-346159. FIGS. 1A and 1B shows temporally consecutive frame images which are obtained by shooting a person. The frame image A10 shown in FIG. 1A is an image obtained by shooting a person A11 who moves toward right. A rectangle A12 is a circumscribed rectangle including head and body of the person which are detected, using motion vectors, as areas with small movement (i.e. steady human area) in the whole body. Similarly, in a frame image A20 shown in FIG. 1B, a circumscribed rectangle A22 of the steady human area detected from a person A21 is presented in a dashed line. In a frame image A30 shown in FIG. 1C, the steady human areas of the circumscribed rectangles A12 and A22 obtained respectively from the frame images A10 and A20 are displayed at the same time in such a way that they overlap with each other. According to the conventional method, the person A11 and the person A21 are identified as the same person based on how the circumscribed rectangles A12 and A22 overlap as well as a continuity of respective motion vectors.
However, the conventional method, in which a person is searched in positions that are close between the frames, has a problem that, in the case where a detection of the person once fails in a certain frame, it becomes impossible to identify a human image in a frame prior to the failed frame with a human image in a frame following the failed frame, so as to track the person.
With the same method, it is conceivable to identify a human image in one frame with a human image in another frame, using colors and image patterns. Other problems, however, are that a positional change increases due to a movement of a person in the case of using temporally distant frames, and that changes of a direction in which the person stands with respect to a camera, a posing of the person and lighting conditions render it difficult to correspond the human image in one frame with the human image in another frame, even though the persons are the same person.
Therefore, in the case where plural persons appear in an image, when a person to be searched for or tracked is hidden behind another person or an object, or when a normal detection cannot be temporarily carried out in a frame due to changes in the lighting conditions, a problem is that it is no longer possible to continue the search or tracking.